Pesticides are widely used in the United States, particularly in agriculture. Over the last four decades, public controversy has swirled around the government’s regulatory programs, usually in connection with specific pesticides such as dichloro diphenyl trichloroethane (DDT) in the 1960s; Alar1, the plant growth regulator used on apples featured on the CBS newsmagazine ‘‘60 Minutes’’ in the 1980s; and the genetically modified variety of corn, StarLink1, that was illegally introduced into the human food supply. As a consequence, government agencies responsible for regulatingpesticideshavehad todealwith abroadarray of cutting-edge scientific issues.These issues range fromsetting the government’s policies on cancer risk assessment to pioneering work in the field of ecological risk assessment, to defining for the country and for the world how to evaluate the safety of the products of modern biotechnology. This chapter focuses

on the latest addition to this long history of scientific accomplishments-the validation of newassays for evaluating the effects of substanceson the endocrine system and the U.S. Environmental Protection Agency’s (EPA) pioneering efforts to improve chemical risk assessment methodology.